When Dry Dock Is Not the Only Option for A Tail Shaft Seal Replacement
Hidramar Group recently assisted in a stern tube seal replacement on a tanker vessel while afloat.
The vessel had an overall length and breadth extreme of 228.6*32.26m. The project was delivered in our berthing line by a team of 8 from the Hidramar Group Shiprepair Division.
The project schedule was 48 hours, but the Hidramar Group Shiprepair Division managed to complete the project in only 36 hours. This has allowed our client to save money by avoiding 12 more expected hours of downtime, allowing their tanker vessel to be fully operational quicker.
About Shaft Seals:
The shaft seal refers to a sealing element that goes between the stern tube and the rotating shaft that connects the main engine of the vessel with the propeller.
The function of this is to prevent lubrication oil leaking into the sea and to prevent sea water from entering the vessel.
With use, these seals become worn out or wear a groove into the shaft itself wich results in the seal no longer being within the tolerance required to be completely watertight. Usually this wear can be predicted and the seals are changed out during the mandatory dry docking every 3 years.
In this case however, the seals were leaking well before the next dry docking call and so the seals had to be replaced as soon as possible. Since drydocking is an expensive undertaking, we arranged with the client to carry out this operation while afloat. The solution would be to trim the vessel by the bow. This means filling all the forward ballast tanks with sea water and emptying the aft ones so that the propeller is lifted out of the water so that the shaft can be worked on.
What makes this task a challenging one is that the propeller is not removed so the seals have to be bonded together around the shaft from a straight section that is wrapped around the shaft. This can only be carried out by a certified technician from the manufacturer of the system The fact that the entire operation would not be carried out on dry land but on a scaffold while afloat added some complexity to the task.
Tenerife Shipyards assumed the responsibility of preparing all the auxiliary services which had to be carried out before and after the manufacturer’s technicians did their specific task. The scope was:
⦁ Erect a scaffold around the stern tube
⦁ Cut the rope guard to allow access to the seals
⦁ Set up access for the manufacturer.
⦁ Once seals were changed out, reinstall the rope guard
⦁ Remove scaffold
What made the execution a challenge was that there was no immediate access to the propeller. The scaffold had to be erected with only a truck crane with a basket and a dinghy. Nevertheless, our ingenious scaffolding team, using ratchet straps, chain falls and welding scaffold poles to the hull managed to prepare a stable and safe working platform for both the fitters working on the rope guard and the technicians from the OEM.
Again the lack of easy access made this task a challenge as we required the basket on the crane to provide electrical current to the working area for cutting and welding works.
After the completion of the seal replacement the rope guard had to be reinstated and the scaffold removed, again with the only access to the propeller at 22m from the quayside being a crane with a personnel basket.
The added pressure on this occasion was the urgency of departure of the vessel combined with the late hour of completion of the manufacturer. The team had to race against the clock to complete the rope guard installation and remove the scaffold before artificial lighting would be required, all while continuing to ensure a quality result and staying safe.
In the end, we can proudly say the team delivered an outstanding job while facing considerable disadvantages.
Shaft seal replacement while afloat has several key strengths all deriving from the fact that it can be carried out in a short amount of time:
⦁ The docking costs are low since all that is required is a quay with calm waters.
⦁ It is known to have no considerable disadvantages compared to dry docking.
⦁ The only “lost time” is the hours required for the ballasting of the vessel to bring the stern tube out of the water.
Do you have a vessel which needs to have its stern tube seals replaced? Contact Hidramar Group for any kind of all-inclusive repair to the ship.